Microlithography is used for the production of microstructured components such as for example integrated circuits or LCDs. The microlithography process is carried out in what is referred to as a projection exposure apparatus which has an illumination system and a projection objective. The image of a mask illuminated via the illumination system (=reticle) is projected in that case via the projection objective onto a substrate (for example a silicon wafer) which is coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection objective in order to transfer the mask structure onto the light-sensitive coating on the substrate.
In the illumination system, for specific and targeted adjustment of defined illumination settings, that is to say intensity distributions in a pupil plane of the illumination system, besides the use of diffractive optical elements (referred to as DOEs), it is also known to use mirror arrangements, for example as disclosed in WO 2005/026843 A2. Such mirror arrangements include a multiplicity of micromirrors which are adjustable independently of each other and which can each be individually tilted in an angle range of for example typically between −10° and +10°. A given tilting arrangement in respect of the mirrors makes it possible to form a desired light distribution (for example a dipole setting, a quadrupole setting or an annular illumination setting) in the pupil plane, by the previously homogenized and collimated laser light being deflected in the appropriate direction, depending on the respectively desired illumination setting. A corresponding structure is diagrammatically shown in FIG. 22 illustrating a partial region of an illumination system which in the beam path of a laser beam 10 successively includes a deflection mirror 11, a refractive optical element (ROE) 12, a lens 13 (only shown by way of example), a microlens arrangement 14, a mirror arrangement 15, a diffuser 16, a lens 17 and a pupil plane PP. The mirror arrangement 15 includes a multiplicity of micromirrors and the microlens arrangement 14 has a multiplicity of microlenses for specific focusing onto those micromirrors.
When using a DOE, the entire pupil plane can be “spread out” from each point of the laser beam profile by diffraction at the diffractive structures of the DOE, and thus a substantially uniform illumination of the pupil plane can achieved irrespective of the intensity distribution in the laser beam profile. When using a mirror arrangement, variations in the laser beam profile can lead to energy fluctuations in the pupil plane, if, for example, polarization states which are different from each other are set in individual poles of a dipole illumination setting, utilizing different regions of the laser beam profile.
Accordingly, when using a mirror arrangement, for specific targeted adjustment of defined illumination settings, a change in the laser beam profile can undesirably result in non-homogenous illumination of the pupil plane.